Discharge lamps, such as high-pressure mercury lamps or metal halide lamps, have been used as light sources of a projector. In these discharge lamps, the shape of an electrode changes due to a drop in fusibility resulting from consumption of the electrode by discharge or progress of crystallization of the electrode according to an increase in cumulative lighting time. In addition, when a plurality of projections grows in an electrode tip end portion or irregular consumption of the electrode body progresses in accordance with the change in the shape of the electrode, the arc origin moves or the arc length (a length between electrodes) changes. Such phenomena are not desirable because they reduce the luminance of a discharge lamp or cause a flicker phenomenon so that the lifespan of the discharge lamp is reduced.
In an effort to solve the problem, a discharge lamp lighting device driving a discharge lamp using an alternating current that is an alternating current having a stationary frequency into which an alternating current having a frequency lower than the stationary frequency may be inserted (see, for example, JP-A-2006-59790). In addition, a discharge lamp lighting device that supplies a driving current, in which a direct current is intermittently inserted in a high-frequency alternating current, to a discharge lamp is known (see, for example, JP-A-1-112698).
However, in JP-A-2006-59790, there is no change in the method of inserting an AC current having a low frequency, and fine control cannot be performed. In addition, in JP-A-1-112698, only a direct current is intermittently inserted into an alternating current having a high frequency, and the length of the inserted DC component is not finely controlled. Accordingly, there are problems in that the deformation of the electrode projections cannot be sufficiently suppressed, and blackening may occur depending on the state. Therefore, enhancement of the maintenance of the shape of the projections on the tip end portion of the electrode is needed.